Needle fluctuating asymmetry is a sensitive indicator of pollution impact on Scots pine (Pinus sylvestris)

Two indices (FAL and FAW, the relative difference in length or weight of two needles on the short shoot, respectively) reflecting the needle fluctuating asymmetry (FA) of the Scots pine (Pinus sylvestris L.) were measured along a gently sloped air pollution gradient in the Karelian Isthmus, north-west Russia and south-east Finland. An earlier study, based on “traditional” indices (growth, crown transparency and needle discoloration), failed to link vitality of Scots pine stands in the Karelian Isthmus with the depositions of the main pollutants, although ultrastructural modifications in pine needles indicated adverse impact of pollution. We found that among-site variation in size-corrected FA was best explained by the pollution load: FAW increased by 40% and FAL increased by 30% near the city of St. Petersburg (the main polluter in the study region) relative to the distant (nearly unpolluted) sites. This pattern is not an artefact of allometry because mean needle length did not change with pollution. In combination with the data from more polluted regions, our result suggests that needle FA is a sensitive early indicator of the pollution impact on Scots pine.